The present invention relates to tools for mechanical working by the method of plastic deformation and more specifically it relates to tools for finishing internal surfaces of blanks.
The present invention can find a vast field of application in machine building for finishing the internal surfaces of power cylinders, engine liners and precision cylinders in measuring apparatuses.
The invention will prove most effective for machining the internal surfaces of cylindrical or elliptical thin-walled blanks with a comparatively low stiffness.
There is known in the present art a centrifugal-impact tool for machining internal surfaces of revolution in blanks. This tool comprises a solid disc surrounded by a cage which has radial slots arranged uniformly around the circumference and accommodating the working elements in the form of balls. Installed on the bottom of the slots are deflectors which take the forces arising when the balls rebound from the surface being machined after striking the surface under the effect of the centrifugal force.
This known tool is characterized by comparatively large masses of rotating parts which, therefore, have to be accurately balanced. Besides, the points where the balls impinge upon the machined surface and deflectors have to be supplied with a lubricating-and-cooling fluid. The output of the known tool is comparatively low since the contact area of the working elements (balls) with the surface being machined is extremely small.
Another known pulse impact tool for finishing the surfaces of revolution in blanks is installed with a provision for linear motion along the geometrical axis of the surface being machined.
The known tool is designed to machine the external surfaces of revolution by plastic deformation which is accomplished by the impacts of the working elements on the surface being machined. The casing of the tool is a body of revolution provided with a diametrical slot to accommodate the working elements. Also, the casing has a central hole for the passage of the blank. The working elements are constituted by two plates of a high-strength material. On the side facing the blank, the plates have semicylindrical depressions with a radius equal to that of the surface being machined. The surface of these depressions will be referred to hereinafter as "working surface." The working elements are located in the slot of the tool casing with a provision for radial motion to the position where the semicylindrical working surfaces form a cylinder whose axis coincides with the geometrical axis of the hole in the casing. The surface of each plate which is opposite to its working surface is provided with a cylindrical roller soldered along the generatrix of the outer surface of the casing; the diameter of the roller is somewhat smaller than the width of the slot in the casing. Thus, the axis of each roller is parallel to the axis of the working surface of the working element, the distance between these axes being approximately equal to the radius of the external surface of the casing.
The tool casing is surrounded by a cage in the form of a sleeve made integral with an extension which has a hole for the passage of the blank. Pressed into the internal surface of the cage, uniformly around the circumference, are shafts which serve as bodies of revolution. The shaft axes are parallel to the axes of the rollers of the working elements. Part of the shaft surface stands out above the internal surface of the cage to provide contact with the working elements during operation of the tool.
To machine the surface of the blank by the method of plastic deformation tool casing is secured on a hollow spindle of a rotary-swaging machine, coaxially with the spindle. The tool cage is secured immovably. The blank (round bar) is clamped in the collet of the tailstock of the rotary-swaging machine and the end of the blank is inserted into the axial hole of the tool casing.
Then the spindle with the tool casing is set in rotation. The working elements are moved by the centrifugal force from the central axis of the casing until the rollers soldered to them come to the surface of the cage. Moving over the surface of the cage, the rollers impinge periodically on the shafts pressed into the cage. This collision moves the working elements towards the center of the casing and the working elements strike the machined surface of the blank. Inasmuch as the mass and velocity of the working elements are comparatively great but the time of contact with the surface being machined is short, the force of the impact is sufficient to produce plastic deformation of the blank material.
After striking the surface of the blank, the working elements move out again under the effect of the centrifugal force until they collide with the next shaft pressed into the cage. The frequency of impacts depends on the spindle speed and the number of the shafts pressed into the cage. While the tool is in operation, the blank moves linearly and uniformly along the axis of the surface being machined.
In the known tool the zone of collision of the shafts with the working elements and the machining zone of the blank are constantly supplied with a lubricating-and-cooling fluid with the purpose of reducing the temperature which rises due to friction between the surfaces of the above-mentioned elements.
The known tool possesses a number of disadvantages one of which lies in that the working surfaces of the working elements are comparatively large so that plastic deformation of the blank material calls for the application of rather strong forces. As a result, the dimensions of the tool and the mass of its rotating parts are comparatively large and the parts have to be accurately balanced during installation. Also, the shape of the working surface of the working element and the nature of its effect on the surface being machined make it possible to produce only a homogeneous smooth surface whose radius is the same as that of the working surface.
Another disadvantage of the tool lies in the difficulties involved in replacing the worn shafts since they are pressed into the cage.
Still another disadvantage of the tool lies in that it must be constantly supplied with a lubricating-and-cooling fluid because the points of contact between the shafts and the working elements and the machining zone of the blank are considerably heated.
The blanks subjected to machining by the known tool have to be sufficiently stiff.